I don't think they are good for Steem in the long term and i don't think paying for votes on a social media site encourages the overall quality of posts. I am happy to see that their use is falling off.
I can understand that it is an attractive idea while the trending page is still the first page that people see when they enter Steemit being as it is an advertising method. but I believe that it creates a very bad image of what can be found here to newcomers. Seeing a post earning in the hundreds only to open it and find it is shilling a service is not going to help with adoption in the long run..